Mail back-up system

> Mailbox format might not be a bottleneck in this application. It's
> fairly efficient at appending new messages, and that is the only
> common operation being performed on these backup mail spools.
The application is using maildir (that's the normal email server that
is using mailbox).
Maildir because it is esaier to expunge oldest emails to free some
disk space and because thetape backup is cheaper when it come sto
incremental.
Olivier